I don't think it's fair to compare Exadel Flamingo to REST (REpresentational State Transfer). However, this question does surface once in a while, so I've decided to spell out the differences in a table.
|Short description||A style of software architecture for distributed hypermedia systems||An integration framework that extends server-side services (Seam, Spring) to a variety of media platforms (desktop, mobile) and RIA technologies (Flex, JavaFX, Swing, Android, J2ME)|
|Suitability||Media-driven websites. “Atom” is a canonical example of a RESTful protocol||Interactive distributed applications – from chats to ecommerce|
|Supported protocols and formats||POX ( Plain Old XML) over HTTP||Hessian, AMF, Buffers over HTTP|
|Development approach||Procedural, CRUD, primitive types only||OO, services, composite objects, updated in a single transaction|
|Development vocabulary||4 methods: GET, PUT, POST, DELETE||Business services exposed via Seam or Spring|
|Transactions||Not supported||Supported via CallSets|
|Security||No standards for transport- or message-level security||Leverages server-side (Seam/Spring) authentication and authorization|
|Advanced features||Messaging, push, and offline messaging|
The Bottom Line
REST is suitable for the stateless exchange of data based on a simple data model, while Flamingo allows developers to program client-side logic using a familiar OO paradigm with composite objects and calls to services.